This invention relates to Wavelength Division Multiplexed (WDM) systems and, more particularly, to a method of and apparatus for providing a space, wavelength, and time division multiple access optical transmission system.
The recently filed patent application of M. T. Fatehi, X. LaRoche, and K. Sohraby, xe2x80x9cWavelength Division Multiplexed System for Optical Access Rings,xe2x80x9d Ser. No. 09/274,199, filed on Mar. 22, 1999, describes a hubbed ring communications system where all laser sources are located in the central office. In that application, the a premises equipment (hereafter called a station) modulates the unmodulated optical signal CW received from the central office with the information that is being transmitted by the station. When an end user station transmits to another station, it modulates its data on the wavelength. The modulated wavelength is received, then demodulated and the original signal is extracted at the receiving station. Since there is no need for laser sources at the user stations, this method offers great cost advantages over other methods. Since the laser equipment is expensive and need special environmental conditioning, the prior method allows providing high bandwidth to the end users at a very low cost. The application of the prior method however is limited to a single station per wavelength; that is, a particular wavelength is assigned to a station until the network is reconfigured. Therefore, when multiple stations wish to access the same wavelength(s) sourced from the central office, there is the risk of contention among them.
What is needed is a technique to extend the prior method to a multiple station access case to enable many stations to access the same wavelength(s) at any time.
In accordance with the present invention, we enable multiple stations to access the same wavelength(s) sourced from a Local Serving Office (LSO) with contention resolution among the stations. More particularly, we disclose station apparatus for use at a Local Serving Office (LSO) and at one or more stations which are connected over an optical facility. The optical facility includes one or more optical fibers, at least one optical fiber carrying a plurality of optical communication wavelengths, and at least one of said wavelengths divided into multiple time slots. The station apparatus enables Space-Wavelength-Time-Division Multiple Access (SWT-DMA) communications using combination of two or more different communication modes selected from a group including (1) space division multiplexed access (SDMA) mode which selects a fiber of the optical facility, (2) wavelength division multiplexed access (WDMA) mode which selects a wavelength(s) on a fiber, and (3) time division multiplexed access (TDMA) mode which selects time slot(s) of a wavelength.
According to other features, communication mode selection may utilize (1) out-of-band signaling, (2) optical tag signaling, or (3) marker signaling over a wavelength of one or more of the optical fibers.